var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
var base64DecodeChars = new Array(
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
	52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
	-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
	15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
	-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
	41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);

function encode(str) {
	var out, i, len;
	var c1, c2, c3;
	len = str.length;
	i = 0;
	out = "";
	while (i < len) {
		c1 = str.charCodeAt(i++) & 0xff;
		if (i == len) {
			out += base64EncodeChars.charAt(c1 >> 2);
			out += base64EncodeChars.charAt((c1 & 0x3) << 4);
			out += "==";
			break;
		}
		c2 = str.charCodeAt(i++);
		if (i == len) {
			out += base64EncodeChars.charAt(c1 >> 2);
			out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
			out += base64EncodeChars.charAt((c2 & 0xF) << 2);
			out += "=";
			break;
		}
		c3 = str.charCodeAt(i++);
		out += base64EncodeChars.charAt(c1 >> 2);
		out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
		out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
		out += base64EncodeChars.charAt(c3 & 0x3F);
	}
	return out;
}

function decode(str) {
	var c1, c2, c3, c4;
	var i, len, out;
	len = str.length;
	i = 0;
	out = "";
	while (i < len) {
		/* c1 */
		do {
			c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
		} while (i < len && c1 == -1);
		if (c1 == -1)
			break;
		/* c2 */
		do {
			c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
		} while (i < len && c2 == -1);
		if (c2 == -1)
			break;
		out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
		/* c3 */
		do {
			c3 = str.charCodeAt(i++) & 0xff;
			if (c3 == 61)
				return out;
			c3 = base64DecodeChars[c3];
		} while (i < len && c3 == -1);
		if (c3 == -1)
			break;
		out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
		/* c4 */
		do {
			c4 = str.charCodeAt(i++) & 0xff;
			if (c4 == 61)
				return out;
			c4 = base64DecodeChars[c4];
		} while (i < len && c4 == -1);
		if (c4 == -1)
			break;
		out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
	}
	return out;
}


function utf16to8(str) {
	var out, i, len, c;
	out = "";
	len = str.length;
	for (i = 0; i < len; i++) {
		c = str.charCodeAt(i);
		if ((c >= 0x0001) && (c <= 0x007F)) {
			out += str.charAt(i);
		} else if (c > 0x07FF) {
			out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
			out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));
			out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
		} else {
			out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));
			out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));
		}
	}
	return out;
}

function utf8to16(str) {
	var out, i, len, c;
	var char2, char3;
	out = "";
	len = str.length;
	i = 0;
	while (i < len) {
		c = str.charCodeAt(i++);
		switch (c >> 4) {
			case 0:
			case 1:
			case 2:
			case 3:
			case 4:
			case 5:
			case 6:
			case 7:
				// 0xxxxxxx
				out += str.charAt(i - 1);
				break;
			case 12:
			case 13:
				// 110x xxxx 10xx xxxx
				char2 = str.charCodeAt(i++);
				out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
				break;
			case 14:
				// 1110 xxxx 10xx xxxx 10xx xxxx
				char2 = str.charCodeAt(i++);
				char3 = str.charCodeAt(i++);
				out += String.fromCharCode(((c & 0x0F) << 12) |
					((char2 & 0x3F) << 6) |
					((char3 & 0x3F) << 0));
				break;
		}
	}
	return out;
}


module.exports = {
	encode: encode,
	decode: decode,
	utf16to8: utf16to8,
	utf8to16: utf8to16
}
